First, I am only dealing with the steady state here. If you are trying to build muscle (body building) then you would need more protein. If you are pregnant or breast feeding or a child still growing, then protein requirements are higher because you are trying to add protein to your body. This discussion only deals with adults at a relatively stable state.

Proteins are made up of building blocks called amino acids, of which there are about 20 common ones. While we talk about protein requirements, really the body needs amino acids. This makes up about 16% of the weight of protein, so that if you eat 56 grams of steak, you do not get 56 grams of protein, but really require about 6 times more by weight (approximately).